Exemplary embodiments of the present invention relate to a device that modulates light from a light source through a plurality of optical modulators and displays an image. Exemplary embodiments of the invention more particularly relate to an optical display device to increase the luminance dynamic range and the number of gradation levels, and a program and a method to control the optical display device.
The related art includes optical display devices such as an LCD (Liquid Crystal Display), an EL (electroluminescent) display, a plasma display, a CRT (Cathode Ray Tube), and a projector that provide considerably improved picture qualities. Further, the resolution and color gamut are nearing levels almost comparable to human visual perception. Regarding the luminance dynamic range, however, the reproducing range is still nothing more than about 1 nit to 102 nit, and the number of gradation levels is still generally 8 bits. Meanwhile, the luminance dynamic range by human visual perception is about 10−2 nit to 104 nit, and human luminance discrimination capability is about 0.2 nit, which can be interpreted into 12 bits in terms of gradation levels. When images displayed at the present optical display devices are viewed in terms of the visual sensitivity characteristics, the luminance dynamic range is particularly narrow, and the gradation at the shadowed part or highlighted part is insufficient. Accordingly the viewer finds the image wanting reality or strength.
In the field of computer graphics (hereinafter simply as “CG”) for example for movies and games, the related art includes a trend to provide display data with a luminance dynamic range or the number of gradation levels close to human visual perception (hereinafter as High Dynamic Range “HDR” display data) in order to make the graphics look more real. However, the optical display devices to display the kind of graphics do not provide sufficient performance. Further, what should be expressed by the original CG content cannot fully be expressed.
The next generation OS (Operating System) is expected to employ the 16-bit color space, and its luminance dynamic range and the number of gradation levels are considerably greater than the present 8-bit color space. Therefore, there is a demand for optical display devices that can fully take advantage of the 16-bit color space.
Among the optical display devices, a projection type display such as a liquid crystal projector and a DLP™ projector (Digital Light Processing, a trademark of Texas Instruments Incorporated) can display images on a large screen and effectively reproduce more real and dynamic images. In this field of the related art technology, the following proposal has been made in order to address and/or solve the above discussed and/or other problems.
As for a high dynamic range, the related art includes projection type display devices, as disclosed in for example, Japanese Patent Laid Open No. 2001-100689, Japanese Patent Laid Open No. 2002-99250 and Helge Seetzen, Lome A. Whitehead, Greg Ward, “A High Dynamic Range Display Using Low and High Resolution Modulators,” SID Symposium 2003, pp. 1450-1453 (2003), hereinafter “Seetzen”. The related art display devices include a light source, an optical modulator that modulates the luminance in each of the wavelength regions for three RGB primary colors in the wavelength region of the light, and a luminance adjusting element that modulates the luminance in the entire wavelength region of the light. Light from the light source is modulated by the luminance adjusting element to have a desired luminance distribution, and its optical image is formed on the display surface of the optical modulator for color modulation, so that secondary modulated light is projected. The pixels in the optical modulator and the luminance adjusting element are independently controlled in response to first and second control values determined based on HDR display data. As the optical modulator, a transmittance modulating element is used. In the element, pixels or segments can have their transmittances independently controlled, and its two dimensional transmittance distribution can be controlled. A typical example of the element is a liquid crystal light valve. Instead of the transmittance modulating element, a reflectance modulating element can be employed, a typical example of which is a DMD (Digital Micromirror Device).
Now, assume that an optical modulator has a transmittance of 0.2% for dark display and a transmittance of 60% for bright display. The single optical modulator has a luminance dynamic range of 60/0.2=300. The related art projection type display device is comparable to an optical series-arrangement of optical modulators having a luminance dynamic range of 300, and therefore the luminance dynamic range to be achieved is 300×300=90,000. The same applies to the number of gradation levels, and by arranging 8-bit gradation optical modulators optically in series, the number of gradation levels can be greater than 8 bits.
The related art includes other projection type display devices that provide a high luminance dynamic range, for example a projection type display device as disclosed by Seetzen and a display device as disclosed by Japanese Patent Laid Open No. 2002-99250.
In related art documents Japanese Patent Laid Open No. 2001-100689 and Japanese Patent Laid Open No. 2002-99250, an LCD is used as the optical modulator, and an illumination device that can be modulated such as an LED or fluorescent lamp is used as the luminance adjusting element.